The shape of the middle lobe of the right lung may vary greatly because of the varying extent of its surfaces in different specimens and the profuse branching of the two segmental bronchi, arteries and veins. The architecture of the middle lobe is therefore especially difficult to understand. For these reasons, attention must be paid to the arrangements of the veins which separate its segments. Thus, the aim of this study was to investigate the ways in which venous drainage of the middle lobe segments may take place. The studies were performed on 40 organs taken from adult human cadavers of both sexes. The pulmonary vessels and bronchi were filled with Plastogen G, after which corrosion casts were made and skeletonised. The lateral segment (SIV) and the medial segment (SV) of the middle lobe were drained in 55% of specimens by one vein and in 35% of specimens by two separately terminated veins. Considerably less frequently there were 3 veins (7.5% of specimens) and only in 2.5% of specimens — 4 veins. In specimens where the middle lobe was drained by one vein (55%) it was formed by joining the lateral (V4) and the medial (V5) segmental veins. In 32.5% of specimens these two segmental veins were formed by a junction of their typical sub-segmental tributaries, where the posterior sub-segmental vein V4a and the superior sub-segmental vein V5a were intra-segmental veins, whereas the anterior sub-segmental vein V4b and the inferior sub-segmental vein V5b were inter-segmental veins. In the remaining 22.5% of specimens with one vein of the middle lobe we noticed modifications in the course of the bronchi, arteries and veins. In the middle lobes drained by two separate veins (35% of specimens) there were independently running segmental veins, V4 and V5. These were formed by their typical tributaries (15%), whereas in the remaining 20% of specimens there were unusual patterns. Three individual veins of the middle lobe (7.5% of specimens) accompanied the lateral-medial type of bronchial arrangement in 5% of specimens, while in 2.5% of specimens the bronchial pattern was of the superior-inferior type. These veins run so as to form more often two superior and one inferior vein. The venous pattern of the middle lobe was consistent with the bronchial and arterial patterns in 35% of specimens. However, this conformation was present in those organs (32.5% of specimens) where the middle lobe was drained by one vein and only in 2.5% of specimens if there were two veins. If 3 or 4 individually emptied veins were present, we could not find any organ in which the bronchial, arterial and venous pattern would be fully compatible. Thus, the research revealed that convenient conditions for the separation of the segments of the middle lobe of the right lung were present in approximately 1/3 of the middle lobes.
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